Systems have been developed for monitoring characteristics, such as tyre pressure and/or tyre temperature, of the wheels of a vehicle. A wheel mounted unit comprising one or more appropriate sensor(s) is located at each wheel, typically inside the tyre, which measures the relevant characteristic(s) and transmits corresponding information to a remote central monitoring station. It is desirable for the central monitoring system to know the location of the respective wheel mounted units so that the measured characteristics can be associated with the respective wheels. This can be achieved by manually programming the system in a calibration process. It is preferable, however, for the system to be able to automatically determine the position of the wheel mounted units.
One problem with such auto-location of wheel units is the determination of whether the tyre mounted unit is located on the left or right side of the vehicle. One solution to this problem is to determine left or right location by detecting the direction of rotation of a tyre mounted unit that is incorporated into the valve of the tyre. This can be achieved by comparing the phase difference between two shock sensors provided in the valve mounted unit. For valve mounted units this method works well as the unit is always mounted in the same orientation with respect to the wheel (the unit is always orientated with the valve pointed away from the vehicle).
In some systems, however, the wheel unit is mounted on the tyre itself (commonly known as tyre mounted sensors) rather than on the valve. In such cases, there is an added complication; the orientation of the tyre, and the monitoring unit within the tyre, with respect to the wheel and hence the vehicle cannot be assumed. This is a problem in systems where the orientation of the sensors must be known in order to make a correct left/right determination. Once orientation is determined, then the solution using two shock sensors (or equivalent devices) or any other solution that can determine orientation of rotation (clockwise/anticlockwise) can be used to perform left/right determination
It would be desirable to provide improved apparatus and methods for determining the position and/or orientation of a tyre mounted unit in a wheel monitoring system